You can't modify a commit. You can only create a copy of a commit and choose to use different commit metadata and/or content for the copy. If you only choose to have different commit message, PersonIdent on your copy then the copied commit will have a different commit id. tree hashes will be the same on original and copied commit. If original commit had kids and you want to stay with the original topology then you have to create copies of the child commits also modifying their parentid to point to your new copy. Tools like (git filter-branch or [1] ) help you in this complicated process. Be aware that if you do that to a shared repo then all other developers will have problems merging in their commits which are based on the old commit ids.